The cast to value type 'Int32' failed because the materializ

Question

I have this code:

var item = (from se in _db.Events
where se.ID == id
select new PseudoEvent()
{
ID = se.ID,
categoryId = se.Categories.ID,
}).FirstOrDefault();

The "Events" and "Categories" tables have a relationship:
"Events" table > Category_ID = "Categories" table > ID

When i dont select a category for the event the "Category_ID" in the "Events" table stays "NULL" and in my code above i get this error:

The cast to value type 'Int32' failed because the materialized value is null. Either the result type's generic parameter or the query must use a nullable type

How can i fix that so the event item will be shown even if the Category_ID column is null?

Please advise
Thanks

Sanjeeb Lenka · Answer

try this: var item = (from se in _db.Events where se.ID == id select new PseudoEvent() { ID = se.ID categoryId = (se.CategoriesID== null) ? 0 : se.CategoriesID }; }).FirstOrDefault(); here if catagoryid come as null it will assign 0 to it.

nave · Answer

Thanks! this works I have another question related to this issue: How do i update the Category_ID column back to null? On insert or update i use this: getCategory = _db.Categories.Find(id); Events.Categories = getCategory; //add foreign key But if the category is 0 (not selected) i want to update the relationship Category_ID back to null. Try to do it like that: Events.Categories = null; //add foreign key But it doesn't seems to work Please advise Thanks